"Green Acres" it ain't, but we love owning and visiting the Hawksbill Cabin, near Stanley and Luray, Virginia, and a wealth of outdoor activities, including: the "World Famous" Shenandoah River, Shenandoah National Park, Skyline Drive, Luray Caverns, and Massanutten Resort. From time to time we'll post about other stuff, too.
As the number of blog posts grows, we've added a few navigation tools in the right column to facilitate getting around the site.

Ramble On

Friday, February 5, 2010

Litter to Electricity: Process and Byproducts

Today, I want to go back and take another look at how poultry litter would be converted into electricity, drawing from a diagram that can be found on Fibrowatt’s web page, and from some analysis a couple of alert Facebook readers contributed. Besides providing a disposal method and producing electricity, there are a couple of byproducts of the process. After the overview, we can take a quick look at those; this will be a preview to the community outreach post about the Minnesota plant and the discussion of environmental impacts that is going on related to the North Carolina plants right now.

One of the insights that was shared is the similarity of this process to more traditional biomass processes, which is often used alongside coal-firing operations to reduce the amount of coal used. In that process, wood chips with a 45-55 percent would produce 1 megawatt of power from 10,000 tons per year – 350 days of plant operations per year. A 40 megawatt plant, the scale we’ve been using for reference in the Luray analysis, would need 400,000 tons of wood chips per year.

Poultry litter is drier than wood chips, which means more would be required, estimated at 10 to 20 percent more. That means 440,000 to 500,000 tons of litter.

Stopping for a moment here, the first impact to consider is the amount of truck traffic that is going to be required to haul the litter. As I understand it, a semi load of litter will range from 14 to 20 tons, requiring more than 25,000 truckloads a year, up to 70 per day. There is a careful process for covering the payload to limit how much is blown out of the trucks during transit, but that is a substantial increase in traffic that will need to be dealt with.

As far as the economics of trucking, no more than a 50-70 mile haul is likely to be cost effective. Since east and west traffic will come over the mountains, that cuts 20 miles off of the economical range. That describes and area that ranges south to Waynesboro/Stuarts Draft, north to Inwood, WV, east to Culpeper, and west to Bayse and Mathias, WV.

FACT CHECK NEEDED: Does anyone have an idea of whether this area has enough poultry houses to produce 500,000 tons of litter?

As far as litter processing at the plant goes, there are photos of the storage area on the Fibrominn site. A friend estimates that to maintain continuity, and because some storage time increases the efficiency of the litter burn, the fuel pile will cover 3-5 acres. It will smell – it’s poultry litter, not an exotic smell around Page County, but still there will be a lot of it. To be fair again, Fibrowatt has a strategy to manage this, and my review of their material will focus on how their communities responded to the approach.

Next, since the plants will burn the litter, there is the question of emissions. In the rendering I posted yesterday, the smoke stack is prominent, so no doubt some design effort has gone into management of this part of the process. Modern plants have done a lot of work to clean up their act on this issue, and I would expect a well controlled combustion process that provides for minor emissions. We have the Minnesota environmental permit application, so I’ll review that for details, also, a lot of the resistance in North Carolina is focused on this issue, attributing it to a potential increase in acid rain. So there will be more on this topic in a future post.

Aside from electrical power, ash is another output from the process. Using wood chips again as the example, this fuel produces 4 to 5 percent ash, or 225 tons of ash for 10,000 tons of fuel. There are three ways to dispose of this – landfills, which Page County has access to; composting, not likely since there will be 225 tons per day; and using it as fertilizer since it is a good source of potassium and phosphorus. The market value for this material ranges from $25 to $50 a ton.

This post's review of the process revealed and discussed the four major concerns of the communities where biomass plants, like the proposed Fibrowatt plant, are located – trucks, emissions, smells, and emissions. For both the Minnesota and the North Carolina projects, I’ve noted that community outreach efforts were established to educate, inform, and negotiate. Also, as I mentioned above, these are likely the basis of the environmental impact discussions in North Carolina. So our next step on the Hawksbill Cabin blog will be to take a more in depth look at these issues.

You mention the comparison with woody biomass. Often, poultry litter is drier than the woody biomass that is used for large-scale energy generation (as opposed to firewood or sawdust & shavings). Wood chips for use in power plants often come from green wood from forestry operations. So actually, based on moisture alone, less litter would be needed. On the other hand, poultry litter has a lot of dirt/nutrient content from the feed ration and the barn floor. As a result, a Fibrowatt plant may require more litter fuel than wood fuel based on the inert content as opposed to moisture content.

It should be understood that we also use woody biomass as a supplemental fuel as it covers periods when litter deliveries are lower and makes it easier to manage the litter when these are mixed together for storage and conveying to the boiler.

With regard to the transportation, we try to maximize the litter payload and this material is far more dense than wood. We try to reach a maximum payload when transporting litter, well above 14 - 20 ton loads you mention. Furthermore, the transportation side of our business is a point of emphasis as we must meet important poultry industry requirements for our transportation. As a result, we are very involved in the requirements of truck type and enclosed payloads. If you look at our operation in Minnesota, we have tightly covered loads as a basic requirement and these truck tarps are inspected when they arrive at the plant. Tight trucks mean no loss of fuel and no odor problems.

With regard to poultry litter storage. You are right that poultry litter smells, that is why all litter is stored inside a fully enclosed fuel hall. To control odor, we establish what is defined as "negative pressure" to ensure that air flows into the fuel hall, but not out. This is done by drawing our combustion air from within the fuel hall, and thereby destroying these odors in the combustion process. All trucks are unloaded within the fuel hall. Stand outside of a truck delivery door and you can feel the air flowing into the building. Best evidence of the success of negative pressure is that after 2.5 years of operation we have not had an odor complaint. The size of the storage area is far less than you mention because we stack the litter in large piles within the enclosed fuel hall using cranes to move it from delivery, storage, and processing prior to conveying to the boiler building in a fully enclosed conveying system.